On the Interpretation of Assurance Case Arguments

An assurance case provides a structured argument to establish a claim for a system based on evidence about the system and its environment. I propose a simple interpretation for the overall argument that uses epistemic methods for its evidential or leaf steps and logic for its reasoning or interior steps: evidential steps that cross some threshold of credibility are accepted as premises in a classical deductive interpretation of the reasoning steps. Thus, all uncertainty is located in the assessment of evidence. I argue for the utility of this interpretation.